Some image sensors are semiconductor devices which convert an optical image into an electric signal. Two types of image sensors are CCD (Charge Coupled Device) image sensors and CMOS (Complementary Metal Oxide Semiconductor) image sensors.
Compared to a CCD image sensor, a CMOS image sensor may have advantages, such as: (1) a relatively simple driving system, (2) flexibility of scanning system design, (3) a signal processing circuit may be integrated into a single chip enabling to make a product smaller, and/or (4) power consumption is relatively low. Accordingly, CMOS image sensors have many desirable applications, such as DSCs (Digital Still Cameras), PC cameras, mobile cameras, and other similar applications.
Some CMOS image sensors are either 3T type, 4T type, or 5T type CMOS image sensor, depending on the number of transistors in a unit pixel. A unit pixel may include one photodiode and depending on a type of CMOS image sensor at least one transistor (e.g. at least one of a transfer transistor, a reset transistor, a select transistor, and/or a drive transistor). An image sensor may include a microlens for collecting light, a color filter for filtering the collected light, a photodiode for sensing the light passed through the color filter, and at least one transistor electrically connected to the photodiode.